Prior endeavors have been made to accurately sense and control the heated surface of a rotary drum type flatwork ironer. These past devices included mechanical contact between a temperature sensing unit with the surface of the drum. This arrangement inherently created undesirable problems, causing use disruption, when the flatwork being processed would become entangled in the mechanical assembly.
Still other problems resulted when foreign matter lodges between a temperature probe and the drum surface thus producing wide variances in temperatures. It was also found that any physical contact whether external or internally with the surface of the drum would cause excess wear and maintenance in addition to producing unreliable indicated temperatures across the full surface of the drum.
It has likewise been proven impractical to insert a stationary temperature probe within a sealed fluid cavity of a jacketed drum. This was unsatisfactory as once the contained fluid expanded during heating, such expanded fluid would not reflect a true temperature reading over the entire drum surfaces but rather produced a variation in the heated areas.